Recently, magnetic disc devices have been more and more required to have a high density, and the swing arm having a head for reproducing/recording signal mounted thereon has been required to make faster access to the desired track and be positioned on the desired track more accurately (speeding up and enhancement of precision of positioning). It has thus been desired to control the radial resonance frequency of the bearing device for swing arm and eliminate the dispersion of rigidity of the bearing device.
In a controller (e.g., swing arm) having a bearing device incorporated therein, the dispersion of rigidity (resonance frequency) of the bearing device is one of factors causing the drop of efficiency of tuning of servo system. Therefore, techniques and apparatus of predetermining the rigidity (resonance frequency) of the bearing device to fall within a predetermined range have been considered important.
Patent Reference 1 cited below discloses a technique of controlling the radial resonance frequency of a bearing device for swing arm.
Further, Patent References 2, 3 and 4 cited below disclose a technique of determining the axial resonance frequency of a bearing device.
Moreover, Patent Reference 5 cited below discloses a method of producing a bearing device which includes press fitting while measuring the resonance frequency of the bearing device under the application of vibration from a piezoelectric element and terminating press fitting when the resonance frequency thus measured reaches a predetermined value.
[Patent Reference 1]
JP-A-2001-83045 (FIG. 1, page 3)
[Patent Reference 2]
Japanese Patent No. 2882105 (FIG. 1, pp. 4-5)
[Patent Reference 3]
JP-A-2000-146726 (FIG. 1, pp. 4-6)
[Patent Reference 4]
JP-A-2000-74788 (FIG. 1, pp. 4-5)
[Patent Reference 5]
JP-A-6-344233 (FIG. 1, pp. 4-6)
However, in accordance with the prior art apparatus and methods of producing a bearing device, the rigidity of the bearing device in the radial direction (radial rigidity) can difficultly be directly evaluated.
In particular, the radial resonance frequency of a small-sized and light-weight bearing device such as bearing device for swing arm can difficultly be accurately measured because such a bearing device has a high resonance frequency attributed to radial rigidity and a small amplitude of resonance peak and the vibration mode of the measuring instrument system and the bearing device are superposed on each other. Further, when the resonance frequency of a plurality of vibration modes (radial translation mode, conical mode) of the bearing device in the radial direction are close to each other, the accurate resonance frequency cannot be determined, making it impossible to accurately evaluate radial rigidity.
Further, in accordance with the apparatus and method disclosed in Patent Reference 5 cited above, the resonance frequency of the pivot can be difficultly extracted from the vibration characteristics of the entire production device comprising the pivot to determine radial rigidity or resonance frequency in particular. The small size and light weight give an extremely high resonance frequency which, too, is a factor making this job difficult. This causes dispersion of resonance frequency, making it likely that the quality of the product thus produced can be unstable.
The present invention has been worked out under the circumstances and its aim is to provide a bearing device producing apparatus and method capable of producing a bearing device while accurately determining the radial rigidity thereof